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Old 05-09-2003, 06:38 AM   #1
mawdryn
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Question what is a zero route ?


Hi,

I recently installed redhat 9 on my router/firewall system and found that there is an extra route (169.254.0.0) associated with eth0,eth1 and lo ... This is being implemented by the ifup script.

It doesn't appear to be interfering with my connection.

Can anyone please tell me what a zero route is and do I need it?

Thanks.
 
Old 05-09-2003, 07:28 AM   #2
baldy3105
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Um, the 169.254.0.0 route come from what I thought was a peice of Windows proprietary behaviour whereby if an interface is configured for DHCP and it fails to get an address it will default to an address in the 169.254.0.0 range.

The range is a reserved address range call Link-Local. These routes are never supposed to be advertised by a router. The remaining digits of these addresses are normally derived from the mac address making it as unique as is possible within the 65,535 range possilble.

I would guess that the route to 169.254.0.0 pointing to an interface means that you are configured for DHCP but have not picked up an address, I must admit I didn't realise that Linux has started doing this, maybe its a part of the DHCP standard, I haven't read it for years!!

A zero route, or all-zero's route or default route is a route that looks like this -

0.0.0.0 0.0.0.0 <gateway IP>

or

default 0.0.0.0 <gateway IP>

It is a catch all route that allows packets to be forwarded by a router if it has no specific route for a destination. It is a routers equivalent of a hosts default gateway.

The confusing thing about Linux, and windows come to that, is that while most things it does and the basic configuration looks like an IP host, in actual fact the OS's carry a route table like a router. So when you define a default gateway the info actually is recorded as a default route.

You only need one if you have a router on your network. Otherwise don't worry. If yo are using dial-up, a default-gateway (default route) will be dynamically configured for you by your ISP.

Hope this helps
 
Old 05-09-2003, 09:24 AM   #3
mawdryn
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Hi,

Thanks for the info.

How would I go about disabling dhcp on redhat 9.. there is no dhcpd running in the process list and the logs have no entries regarding dhcp allocation (failed or otherwise).

I'm running static ip's on all my systems, so I don't need it running.
 
Old 11-21-2012, 11:57 AM   #4
tek_rspns
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169.254.x.x convention

I found the following information posted at linuxstories on blogspot.com to be very illuminating. The 169.254.x.x subnet is apparently an IETF workgroup convention more than it is a DNS standard. See below:

Monday, February 14, 2011

Zero Configuration Network (ZEROCONF)

Most Linux distributions utilise the Zero Configuration Network (ZEROCONF) automation suite. This is an IETF workgroup that planned and coordinated a series of dynamic configuration protocols to allow many operating systems to automatically configure themselves and communicate on a network without the need of DHCP or DNS servers. ZEROCONF utilises the 169.254.0.0/16 network address to autoconfigure using a series of unanswered "ARP" queries and then assumes an address if the queries yield an empty result.

A route to the ZEROCONF network is added to the routing table by the network initscripts.

[bash]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.214.64.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1 <-- ZEROCONF default IP route
0.0.0.0 10.214.64.254 0.0.0.0 UG 0 0 0 eth0

ZEROCONF can be turned off by adding the following entry to the "/etc/sysconfig/network" configuration file.

[bash]# vi /etc/sysconfig/network
NOZEROCONF=yes


The value for the "NOZEROCONF" parameter can actually be set to any value, the initscripts only check to determine whether the parameter has zero length. So setting "NOZEROCONF=no" will have the same effect as setting it to "yes". You will need to comment or remove the variable to reactive ZEROCONF.

The networking service will need to be restarted before the changes will take effect.


[bash]# /etc/init.d/network restart

Checking the network routing table again will identify the ZEROCONF route has been disabled and removed from the routing table.

[bash]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.214.64.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
0.0.0.0 10.214.64.254 0.0.0.0 UG 0 0 0 eth0

ZEROCONF is also commonly referred to as IPv4 Link-Local (IPv4LL) and Automatic Private IP Addressing (APIPA).
Posted by gpanagou at 2/14/2011 11:17:00 AM

Last edited by tek_rspns; 11-21-2012 at 12:04 PM. Reason: Formatting
 
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